1. Field of the Invention
The present invention relates to a pacer system which is adapted to alter the rate of the pacer pulses delivered (rate of pacing pulses delivered by an artificial pacemaker) to the heart while an individual is exercising utilizing the systolic pressure or its time derivative sensed in the right ventricle to obtain a required cardiac output.
2. Description of the Prior Art
Heretofore patients with heart dysfunctions or heart disease such as sinus node disease have been able to live a relatively normal life with the implantation of an artificial pacemaker often referred to as a pacer. However, such pacers have not always been able to mimic the response of a normal healthy heart. A normal heart responds to exercise and stress by increasing cardiac output through increased heart rate or stroke volume.
In this respect, patients with sinus node disease have lost the ability to increase heart rate with exercise. Accordingly, it has become a goal of optimal pacing to provide exercise responsiveness in a pacer by sensing the need for increased cardiac output.
With a view toward obtaining this goal, a number of pacemakers have been proposed for indirectly sensing the need for increased heart rate by sensing P-waves, nerve impulses, Q-T interval, pH, oxygen saturation, respiratory rate, stroke volume, motion, atrial pressure and temperature.
A P-wave triggered artificial pacemaker adapted to be exercise responsive by responding to average atrial rate has been proposed in the Knudson & Amundson U.S. Pat. No. 4,313,442.
An artificial pacemaker responsive to changes in the Q-T interval is proposed in the Rickards U.S. Pat. No. 4,228,803.
A proposal for placing electrodes on the Hering's nerve that originate from receptors in the sinus and glomus carotids is disclosed in the Gonzalez U.S. Pat. No. 4,201,219.
Pacers for sensing blood pH are proposed in the Alcidi U.S. Pat. No. 4,009,721 and the Mauer et al U.S. Pat. No. 4,252,124.
An artificial pacemaker that senses oxygen saturation at the tip of a catheter in the right ventricle is proposed in the Wirtzfeld et al U.S. Pat. No. 4,202,339.
Another artificial cardiac pacemaker which increases pacing rate in accordance with an increase in respiration rate is proposed in the Krasner U.S. Pat. No. 3,593,718.
Pacers for sensing motion or mechanical activity are proposed in the Dahl U.S. Pat. No. 4,140,132 and the Anderson et al U.S. Pat. No. 4,428,378.
Another artificial cardiac pacemaker responsive to exercise by sensing venous blood temperature in the right ventricle of the heart is proposed in Cook et al U.S. Pat. No. 4,436,092.
In a healthy heart, the sympathetic nervous system activates the sinus node to increase its frequency. Secondly, it activates the heart to increase its dynamic contraction during exercise. The first activation is lost in patients with sinus node disease but the second phenomenon of dynamic contraction still exists. This means that exercise modified increased sympathetic activity can be detected by measuring the right ventricular systolic pressure. As will be described in greater detail hereinafter, the apparatus of the present invention utilizes the right ventricular systolic pressure or the time derivative thereof to control the pacing rate of an implanted artificial pacemaker.
Heretofore it has been proposed to sense pressure in the right atrium and to utilize the pressure sensed to control pacing of an electrode in the right ventricle in the Cohen U.S. Pat. No. 3,358,690.
Also, the Zacouto U.S. Pat. No. 3,857,399 discloses, in FIG. 19 thereof, a pressure sensor that measures either left ventricular pressure or intramyocardial pressure. One sensor is located in the myocardium or septum and the other sensor is located in the left ventricle. Apparently, the pacer coupled to these sensors responds to average base pressure over relatively long periods of time and the pacer system disclosed therein appears to be static and slowly responsive to exercise.
In the field of artificial hearts, it has been proposed in the Purdy U.S. Pat. No. 3,828,371 directed to a self contained artificial heart, to control operation of the artificial heart relative to the sensing of atrial pressure.
Further, there is disclosed in U.S.S.R. Inventor's Certificate No. 858,843 a device for controlling a prosthesis of the heart which replaces a natural heart and which comprises a servomechanism responsive to blood pressure in the atrium of the heart.
The apparatus of the present invention can utilize a piezoresistive pressure sensor for sensing right ventricular systolic pressure and a number of different piezoresistive pressure sensors for use in measuring blood pressure have been proposed. Also other blood pressure sensing devices or blood pressure operated devices have been proposed. See for example the pressure sensors and transducers disclosed in the following U.S. patents:
______________________________________ PATENTEE ______________________________________ U.S. PAT. NO. 2,634,721 Greenwood, Jr. 2,976,865 Shipley 3,088,323 Welkowitz et al 3,294,988 Packard 3,563,245 McLean 3,906,960 Lehr 4,432,372 Monroe Published European Patent Application 0 080 347 to Anderson et al ______________________________________
The apparatus of the present invention differs from the previously proposed apparatus by providing an implanted artificial pacemaker having a microprocessor therein with a program or algorithm stored in the microprocessor for controlling the pacing rate of pacing pulses supplied to an electrode at the end of a pacing lead in the right ventricle relative to, and in response to, the right ventricular systolic pressure or the time derivative thereof obtained from a pressure sensor mounted on the pacing lead and located in the right ventricle.